Trunk position circuit for carrier frequency communication systems



April 21, 1942. H. NITZ 2,280,538

TRUNK POSITION CIRCUIT FOR ARRIER FRE UENCY COMMUNICATION SYSTEMS Filed Nov. 27, 1940 Patented Apr. 21, 1942 TRUNK POSITION CIRCUIT FOR CARRIER FREQUENCY COMMUNICATION SYSTEMS Herbert Nitz, Berlin, Germany, assignor to C. Lorenz Aktiemgesellschaft, Berlin-Tempelhof, Germany, a company Application November 27, 1940, Serial No. 367,416 In Germany December 8, 1939 2 Claims.

In telephone exchanges the trunk lines terminate in so-called trunk positions. In the case of transmission of intelligence eifected in carrier frequency fashion such trunk positions must be arranged so that the operators inquiry toward the trunk line side may be in carrier frequency fashion without the aid of a split connection or forked circuit whereas the connecting through from the trunk position to the subscriber is effected in the usual low frequency fashion.

One embodiment of the present invention has a high-pass filter and a demodulator included in the equipment of the trunk position.

Arrangements as provided by the invention fulfill the aforesaid requirements. When the desired connection has been established the subscribers apparatus can be automatically switched in the trunk exchange in a manner to become arranged for carrier frequency reception. The preliminary intercommunication between trunk position and local subscriber, however, is in low frequency fashion.

The drawing shows a diagram of one embodiment of the invention and illustrates how a trunk position is connected to a carrier frequency terminal circuit.

I, 2 denote the two-wire line arriving from such terminal circuit. 3 indicates a high-pass filter, 4 a highly resistive demodulator, 5 the telephone receiver, and 6 the microphone of the operators set. This telephone set can be switched with the aid of contacts 8, 9 actuated by means of a switch 1 movable either in direction A or in direction B. Direction A enables the operator to inquire over the trunk line while direction B is for inquiring the subscriber.

In the circuit arrangement of the trunk position the self-attenuation of the operators telephone set is. diminished in both directions through the avoidance of a split connection or forked circuit.

When switching over for carrier frequency inquiring, resistance R which in the low frequency operation is necessary for tuning the bridge connection, is short-circuited by contact I0.

What is claimed is:

1. In a trunk position for trunk lines with carrier frequency terminal circuit, an operators telephone set, switching means to connect this telephone set either to the trunk line in the case of carrier frequency inquiring, or to a subscribers apparatus in the case of low frequency inquiring,

a resistance for tuning in the case of low fre-' quency operation, and means under control of said switching means to short-circuit this resistance in the case of carrier frequency inquiring.

2. In a trunk position as defined in claim 1, a high pass filter and a demodulator included in the operators set.

- HERBERT NITZ. 

